add setWindowFlags(Qt::Window) to improve window management

* improves window handling a lot
	(on Linux GNOME 3 at least: quickly resizing windows left/right, not forced in foreground anymore etc.)
	setWindowFlags() inserted in all *window.cpp files except mainwindow
    * some whitespace at EOL trimmed

re/sniffer/snifferwindow.cpp

@@ -13,6 +13,7 @@ SnifferWindow::SnifferWindow(QWidget *parent) :
     mFilter(false)
 {
     ui->setupUi(this);
+    setWindowFlags(Qt::Window);
     ui->treeView->setModel(&mModel);
 
     /* set column width */